In laundering it is common to treat various types of fabrics such as wool, cotton, silk, nylon, polyester, permanent-press, and the like with chemicals which are fabric-conditioning or treating agents to render the fabrics soft to the touch, to reduce tangling, knotting or wrinkling, to render them free of static electricity, to render them bacteria-resistant, to deodorize them, and to otherwise condition them. The use of fabric conditioners permits dried clothes to be sorted and folded more easily and quickly. These results historically were achieved by introducing an aqueous solution or dispersion of a fabric-conditioning agent into the wash water during the wash cycle of the laundry process or by introducing such an aqueous solution or dispersion of fabric-conditioning agent into the rinse water during the rinsing cycle of the laundry process. In addition to the inconvenience of measuring out a liquid material, there can be a number of drawbacks associated with the use of fabric-conditioning agents during the laundry rinse cycle, including the need to remember when to add the material in the case of those washing machines which have no automatic dispenser. Other drawbacks include waste of material and adverse ecological effects (from fabric softening material lost to the drain), the possibility of redeposition of soil during the deep rinse cycle, and the possibility of undesirable interactions between anionic detergents and cationic softeners.
While the use of liquid fabric-conditioning agents in machine dryers has been suggested, the idea has not gained widespread commercial acceptance probably because of such factors as the need for complex dispensing equipment.
To overcome the problems associated with using fabric-conditioning agents during the wash or rinse cycle or with using liquid fabric-conditioning agents during the drying cycle a number of means and techniques have been developed for dispensing fabric conditioners in machine laundry dryers.
Spray systems have been devised for spraying fabric softening agent into a dryer drum before putting fabrics into the dryer so that the fabric-conditioning agent will rub off the drum onto the fabrics during the drying process; however, this can lead to the build up of sticky residue on the inside of the dryer drum, leading to corrosion of the drum. Such residues can also cause plugging of the vent filters.
Means and techniques for dispensing solid fabric conditioners in machine dryers have also been developed. For example, flexible substrates coated or impregnated with fabric softening agents have been designed for use with machine dryers and are currently commercially available. For example, see U.S. Pat. Nos. 3,686,025 (Morton) issued Aug. 22, 1972; 3,632,396 (Perez-Zamora) issued Jan. 4, 1972; and 3,442,692 (Gaiser) issued May 6, 1969. Articles of commerce based on this patented technology have generally been pre-measured, single-use, disposable sheets which can be expensive to use. Another problem associated with these coated or impregnated substrates has been the possibility that they may mark or stain clothes in the dryer. One way to decrease the possibility of marking and staining has been to coat the flexible substrate with a solid softening composition which will remain solid throughout the normal operating temperature range of a dryer (e.g. 45-80.degree. C.). The flexing of the flexible substrate which accompanies the tumbling action of a dryer drum is presently believed to cause the coating of the chemical agent to develop a flaking action, resulting in the transfer of the agent to the clothes in the form of tiny solid flakes or crystals. These flakes of solid agent are considered less likely to cause staining as compared to an agent which is molten or significantly softened within the 45-80.degree. C. range. This coated flexible substrate approach is believed to be best suited for single-use flexible sheets which are separated from the dryer load after the drying cycle and then discarded.
Attaching coated substrates to the interior of the dryer drum, instead of allowing them to tumble freely in the dryer, has also been suggested. For example, see U.S. Pat. No. 3,634,947 (Furgal) issued Jan. 18, 1972. This technique eliminates the need to sort through the dried fabric to locate the substrate which is to be discarded.
More recently, reusable permeable dispensers for dispensing solid or semi-solid fabric-conditioning agents which can either be attached to the dryer drum or tumbled loosely in the dryer have been developed. For example, see U.S. Pat. Nos. 3,870,145 (Mizuno) issued Mar. 11, 1975; 3,948,387 (Haertle) issued Apr. 6, 1976; 4,004,685 (Mizuno et al) issued Jan. 25, 1977; and 4,014,432 (Clothier et al) issued Mar. 29, 1977. These dispensers have generally used conditioning agents which are solid at room temperature and which soften and permeate the dispenser when heated to the operating temperature range of dryers. A broad softening point range for the conditioning agent used in desirable and has been obtained by using a blend of coconut monoethanolamide (melting point of 62-65.degree. C.) dimethyl di (hydrogenated tallow) ammonium chloride (melting point of 139-144.degree. C.), and stearyl dimethyl benzyl ammonium chloride (melting point of 59-65.degree. C.) to form a mixture having a softening point range of 53-85.degree. C. For example, see Example I of U.S. Pat. No. 4,004,685 (Mizuno) issued Jan. 25, 1977. Dispensers of this type have been generally produced by mixing the individual ingredients in their solid state to form a powdered mixture which is used to fill cloth bags having a permeable surface. A filled bag is then heated to cause the powdered mixture to soften and to fuse together, the composition is then cooled to form a hard bar of fabric softener which adheres to the walls of the bag.
If the fabric softener does not sufficiently permeate the permeable surface during the heating step or if additional steps are not taken to assure sufficient permeation, the dispenser may not dispense sufficient softening agent during its initial use; one or more drying cycles being required to cause the softening agent to sufficiently permeate the bag so that a sufficient quantity will be dispensed during a drying cycle. A problem associated with a production process utilizing powder fills has been the inconsistency of fill from bag to bag, which occurs when volumetric filling is used, because of the compressibility of the powder. Another problem with powder filling is that segregation of the individual ingredients may occur prior to filling and cause the percentage of the ingredients to vary from bag to bag.
At the normal operating temperature of many dryers (e.g. 50-90.degree. C.), it has been shown in U.S. Pat. No. 4,004,685 that extremely well-controlled metering of the fabric-softening agent occurs, thereby permitting reuse for a large number of cycles (e.g. more than 5 or 10 cycles) with the assurance that a uniform amount or dosage of fabric softener will be dispensed to each load placed in the dryer--at least after the first two or three cycles of use. However, in recent years machine dryers have become more sophisticated and may be provided with "air-dry" and delicate fabric cycles which use drying temperatures ranging down to room temperature (20-25.degree. C.). On the other hand, if the operating thermostat of these sophisticated dryers should fail, so that only the safety thermostat is operative, drying temperatures above 90.degree. C. may occur, e.g. 100.degree. or even 120.degree. C. Thus, these sophisticated machines may require a fabric softener dispensing means with greater flexibility including the ability to dispense softening agents at broader temperature ranges without increasing the danger of marking and staining at higher drying temperatures.